Energy and Power in Electric Circuits – Learn

Potential difference is defined as the work done to move a charge against an electric field between two points. The equation relating potential difference and work is:

or

Where:

= voltage (in V)

= work (in J)

= charge (in C)

The rate at which energy is used or converted into other forms of energy over a period of time is known as its electrical power. Power (P) is the rate at which energy is transformed in a circuit component, and is measured in watts (W). Power is calculated using:

Where:

= power (in W)

These equations are often rearranged to give the relationship:

Example 1:

Calculate the work carried by 4C of charge with a potential difference of 12V:

Using:

Example 2:

A speaker operating on a voltage of 18V draws a current of 3A. Calculate the power used by this speaker:

Using

Example 3:

A potential difference of 6V is used to produce a current of 150mA in a set of headphones for 10 minutes. How much energy is used in this time?